Heat-resistant, high-speed, high-load rolling bearing and grease composition

ABSTRACT

A heat-resistant, high-speed, high-load rolling bearing for automotive accessories and electric part is provided which develops no abnormal flaking and is sufficiently long in life and superior in durability. It is a heat-resistant, high-speed, high-load rolling bearing in which is sealed a grease composition which comprises a base oil which is a mixture alkyldiphenyl ether oil and aromatic ester oil at the ratio (in weight) of 50:50 to 80:20, a diurea compound expressed by the following formula as a thickening agent, and 0.1 to 5 wt % of a passivating agent.  
                 
 
     (wherein R 2  is an aromatic hydrocarbon group having a carbon number of 6-15, R 1  and R 3  are an aromatic hydrocarbon groups having a carbon number of 6-12 or a cycloaliphatic hydrocarbon group having a carbon number of 6-20. R 1  and R 3  may be identical to or different from each other.)

BACKGROUND OF THE INVENTION

[0001] This invention relates to a heat-resistant, high-speed, high-load rolling bearing used for accessories or electric parts of an automobile and a grease composition for rolling bearings used to support a rotary shaft of accessories or electric parts of an automobile.

[0002] With increasing requirements for compactness, lightness and quietness of automobiles, compactness and lightness of electric parts and accessory parts (hereinafter simply referred to as electric accessories) such as air-conditioners and electric fans and closedness of engine rooms are seeked. For the performance itself of devices, requirements for high output and high efficiency increase. A method is used in which lowering of the output resulting from compactness of electric accessories is compensated for by increasing the speed of rotation.

[0003] But if rolling bearings for electric accessories are used with a conventional grease under high-speed, high-load conditions, flaking tends to occur on the rolling surfaces, so that the life of the bearings expires prematurely.

[0004] Unlike ordinary flaking on the surface or in the superficial layer of the rolling surface caused by metal fatigue, flaking causing shortening of the life is a peculiar destructive phenomenon (hereinafter referred to as abnormal flaking phenomenon) that suddenly develops from a fairly deep portion.

[0005] As measures against such abnormal flaking, in JP patent publication 1-259097, a grease is disclosed in which the base oil is alkyldiphenyl ether and a thickening agent is a diurea compound having an aromatic hydrocarbon group at ends.

[0006] Although this conventional grease does not develop abnormal flaking under high-speed, high-load conditions, it is inferior in flowability. Thus, it is difficult to supply the grease sufficiently to rolling surfaces. Thus, for rolling bearings in which is sealed the grease, a sufficient durability is not expected when they are used under high-speed, high-load conditions.

[0007] As a technique for solving this problem, JP patent publication 2557597 proposes to seal in a rolling bearing a grease composition which comprises a base oil in which alkyldiphenyl ether oil and poly-α-olefin oil are blended at the ratio (in weight) of 20:80 to 80:20, and which has a dynamic viscosity at 40° C. of 51-73 cSt, 5-40 wt % of an aromatic diurea compound or an aromatic urea•urethane compound as a thickening agent, and further a passivating oxidant and an organic sulfonate.

[0008] But rolling bearings having such a grease sealed therein have insufficient high-temperature endurance for use in electric accessories which are made compact. E.g. continued use for 200 hours or longer at a speed of 10000 rpm at a temperature of 150° C. was impossible.

[0009] The JP patent publication 9-3466 discloses a grease composition for rolling bearings used for automotive electric parts and accessories, the grease composition comprising a base oil which is a mixture of dialkyldiphenyl ether oil and an aliphatic ester synthesized oil or a poly-α-olefin oil, and a thickening agent which is a diurea compound having an aromatic hydrocarbon group at ends. But the grease composition had poor endurance for use under high-temperature high-speed conditions.

[0010] A first object of this invention is to provide a heat-resistant, high-speed, high-load rolling bearing used for accessories and electric parts of automobiles, which will not develop abnormal flaking and which has a sufficiently long life and a superior durability under high-temperature, high-speed, high-load conditions.

[0011] A second object of this invention is to provide a grease composition for rolling bearings used to support rotary shafts of automotive accessories and electric parts, which develops no abnormal flaking and has a sufficiently long life and a superior durability under high-temperature, high-speed and high-load conditions.

SUMMARY OF THE INVENTION

[0012] According to this invention, there is provided a heat-resistant, high-speed, high-load rolling bearing in which is sealed a grease composition which comprises a base oil which is a mixture of alkyldiphenyl ether oil and aromatic ester oil at the ratio (in weight) of 50:50 to 80:20, a diurea compound expressed by the following formula as a thickening agent, and 0.1 to 5 wt % of a passivating agent.

[0013] (wherein R₂ is an aromatic hydrocarbon group having a carbon number of 6-15, R₁ and R₃ are an aromatic hydrocarbon groups having a carbon number of 6-12 or a cycloaliphatic hydrocarbon group having a carbon number of 6-20. R₁ and R₃ may be identical to or different from each other.)

[0014] Because the lubricating grease having such a composition uses alkyldiphenyl ether oil which is superior in heat resistance and is less likely to develop abnormal flaking, and an aromatic ester oil which is superior in heat resistance and is good in flowability, as basic oils, it is extremely superior in properties of being supplied to frictional surfaces, so that sufficient durability is assured even if the bearing is used under high-speed, high-load conditions.

[0015] By adding a passivating agent to the aromatic ester oil which is superior in heat resistance and good in flowability, a passivated film is formed under high-temperature, high-speed, high-load conditions. This prevents abnormal premature flaking. Also, due to another function of the passivating agent of “preventing oxidative deterioration of grease or lubricating oil during high-temperature use”, the durability of the aromatic ester oil dramatically improves under high-temperature, high-speed conditions.

[0016] This function of “preventing oxidation of grease or lubricating oil during high-temperature use” exhibits a large effect if a passivating agent is added to a lubricating oil which has aromatic rings and is superior in heat resistance. Thus, with a rolling bearing in which is sealed the grease composition, abnormal flaking will not develop, its life is extended under high-speed, high-load conditions, and durability under high-temperature conditions is superior.

[0017] A preferable conditions for providing a heat-resistant, high-speed, high-load rolling bearing that will not develop abnormal flaking and is superior in durability is that the aromatic ester oil used has a dynamic viscosity at 40° C. of 20-150 mm²/s.

[0018] In order to solve the second object, according to this invention, there is provided the abovesaid grease composition for a rolling bearing of an automotive accessory or electric part.

[0019] Since the grease composition contains the predetermined base oil and the predetermined thickening agent, it ensures that a heat-resistant lubricating oil is sufficiently supplied to frictional surfaces even under high-temperature, high-speed, high-load conditions, and thus ensures a long life when used in an automotive accessory or electric part such as an alternator, an electromagnetic clutch, a tension pulley or a one-way clutch. Also, since a predetermined amount of a passivating agent is added to the grease having such properties, no abnormal flaking will develop under such use conditions. Thus a grease composition in provided which is superior in durability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] The alkyl diphenyl ether oil used in this invention is obtained by addition reaction of 1 mol of diphenyl ether with 1-3 mols of α-olefin having a carbon number of 10-22.

[0021] The aromatic ester oil used in this invention is an alkyl ester of trimellitic acid or pyromellitic acid. The alkyl group is one having a carbon number of 4-18. Specifically, butyl group, pentyl group, hexyl group, octyl group, nonile group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, hexadecyl group, heptadecyl group, octadecyl group, etc. can be cited. These alkyl groups may have linear chains or branched chains. In the alkyl ester, the alkyl groups may be identical or different from each other.

[0022] Compared to ester oils such as poly-α-olefin oil, polyol ester oil and diester oil, the aromatic ester oil is superior in heat resistance and less liable to evaporation and oxidative deterioration at high temperature. Thus it can be used for long hours at high temperature.

[0023] The ratio of the alkyldiphenyl ether oil and aromatic ester oil used as the base oil in this invention should be 50:50 to 80:20. If the aromatic ester oil in the base oil is less than 20%, the flowability would be inferior. This worsens supply of the grease to the rolling surfaces of the bearing, so that a sufficient durability would not be obtained under high-speed, high-load conditions. If the aromatic ester oil in the base oil exceeds 50%, abnormal flaking tends to occur under high-speed, high-load conditions.

[0024] Next, as the thickening agent used in this invention, a diurea compound expressed by the following formula is used.

[0025] (wherein R₂ is an aromatic hydrocarbon group having a carbon number of 6-15, R₁ and R₃ are an aromatic hydrocarbon group having a carbon number of 6-12 or a cycloaliphatic hydrocarbon group having a carbon number of 6-20. R₁ and R₃ may be identical to or different from each other.)

[0026] As the cycloaliphatic hydrocarbon groups having a carbon number of 6-20, for example, cyclohexyl groups or cyclohexyl derivatives may be used.

[0027] As the aromatic hydrocarbon groups having a carbon number of 6-10, for example, phenyl group, toluic group, xylyl group, t-butylphenyl group, benzyl group, etc. may be used. A monovalent aromatic hydrocarbon group is especially suitable.

[0028] A specific example of R₂ in the above formula is a compound expressed by the following formula, but is not particularly limited if it is an aromatic hydrocarbon group of a chemical structure which is superior in heat stability and oxidation stability.

[0029] The rate of the aromatic hydrocarbon group relative to the total amount of R₁ and R₃ in the diurea compound should preferably be 50-100 mol%. If the rate is less than 50 mol %, resistance to abnormal flaking would not be sufficient.

[0030] The amount of the diurea compound as the thickening agent in this invention should be preferably 5 to 30 wt %. If less than 5 wt %, resistance to abnormal flaking would be insufficient. Also, leakage of grease from the bearing might increase. If over 30 wt %, durability of the bearing at high temperature and high speed would markedly worsen. Also, abnormal rotating sound may occur at low temperature.

[0031] Next, the passivating agent used in the present invention is an oxidizing agent that passivates metallic surfaces of steel of which rolling bearings for electric accessories are made. For example, an inorganic corrosion preventive agent of a cathode bipolar type such as a nitrite, nitrate, chromate, phosphate, molybdate or tungstate may be used. Among them, sodium nitrite is preferable.

[0032] These passivating agents passivate metallic surfaces, thus improving flaking resistance and corrosion preventive ability. Also, it has been found out that these passivating agents have the function of preventing oxidative deterioration of grease when used at high temperature and dramatically improving the durability of grease under high-temperature conditions.

[0033] This function has a large effect if the passivating agent is added to a lubricating oil having aromatic rings, which is especially superior in heat resistance. By adding it to an aromatic ester oil or an alkyldiphenyl ether oil, durability of the grease under high-temperature conditions dramatically improves.

[0034] The content of such a passivating agent should be 0.1 to 5 wt %. If it is less than 0.1 wt %, the effect would be insufficient. If 5 wt % or over, it would have a bad influence on the acoustic properties of the bearing.

[0035] To the grease composition according to this invention, known additives may be added as necessary to improve its excellent performance. Such additives include thickening agents such as metallic soap, Penton and silica gel, antioxidants such as amine family, phenol family, phosphorus family ones and zinc dithiophosphate, extreme pressure agents such as zinc dithiophosphate and organic molybdenum, oily agents such as fatty acids and vegetable oils, rust preventives such as metallic sulfonate, dinonylnaphthalene sulfonate and sorbitan ester, metal inactivating agent such as benzotriazole, viscosity index improvers such as polymethacrylate, polyisobutylene and polystyrene, etc. Of course, they may be added singly or in a combination of two or more.

EXAMPLES and Comparative Examples Examples 1-5

[0036] A base oil comprising a mixture of alkyl diphenyl ether oil and aromatic ester oil was prepared in the contents shown in Table 1. In half of the base oil prepared, 1 mol of 4,4′-diphenylmethane diisocyanate (MDI) was dissolved and in the remaining half of the base oil, 2 mol of monoamine was dissolved. After adding the latter half to the first half of the base oil while stirring, stirring was continued for 30 minutes at 100-120° C. to react and deposit a diurea compound in the base oil. To it, 2.0 wt % of the antioxidant shown in Table 1 was added and the mixture was stirred for 10 minutes at 100-120° C. Thereafter, the mixture was cooled and after adding a passivating agent at the rate shown in Table 1 and mixing, it was homogenized by use of three rolls to obtain a grease composition.

[0037] The consistency of the grease composition obtained was measured. Also, it was sealed in a rolling bearing and a high-temperature, high-speed endurance test, hard acceleration/deceleration test, high-speed, high-load endurance test were carried out by the below-described test methods. The test results are shown in Table 1.

[0038] {circle over (1)} Worked Penetration: Measured under JIS K2220 5.3

[0039] {circle over (2)} High-temperature, High-speed Endurance Test:

[0040] 0.7 g of each test grease was sealed in a rolling bearing (6204), which was rotated at a speed of 10000 rpm with the bearing outer ring outer periphery temperature of 150° C., radial load of 67 N, and axial load of 67 N to measure the time until seizure occurred.

[0041] {circle over (3)} Hard Acceleration/Deceleration Test:

[0042] This test was carried out for a rolling bearing having an inner ring supporting a rotary shaft for supporting a pulley around which is wound a rotary belt of an alternator as an example of an electric accessory. The test conditions were set to the load on the pulley of 3234 N and the rotating speed of 0-18000 rpm. The durable time (life time) was measured in terms of the time until abnormal flaking occurred in the bearing, so that the vibration detected by a vibration detector increased above a preset value, and the generator stopped.

[0043] {circle over (4)} High-speed, High-load Endurance Test:

[0044] 1.8 g of each test grease was sealed in a rolling bearing (6204) and the outer ring was rotated with the number of revolutions at 10000 rpm under the radial load of 3234 N to measure the time until seizure occurred.

Comparative Examples 1-6

[0045] The base oils shown in Table were prepared, and in half of the base oil, 1 mol of 4,4′-diphenylmethane diisocyanate (MDI) was dissolved, and in the remaining half of the base oil, 2 mol of monoamine was dissolved. After adding the latter half to the first half of the base oil while stirring, stirring was continued for 30 minutes at 100-120° C. to deposit a diurea compound by reaction. To it, the antioxidant shown in Table 1 was added and the mixture was stirred for 10 minutes at 100-120° C. Thereafter, it was cooled and after adding a passivating agent shown in Table 1 and mixing, it was homogenized by use of three rolls to obtain a grease composition.

[0046] The consistency of the grease composition was measured. Also, it was sealed in a rolling bearing and a high-temperature, high-speed endurance test, hard acceleration/deceleration test, high-speed, high-load endurance test were carried out. The test results are shown in Table 1.

[0047] As is apparent from the test results shown in Table 1, Comparative Example 1 to which is added no passivating agent, was inferior in any of the high-temperature, high-speed endurance test, hard acceleration/deceleration test, and high-speed, high-load endurance test.

[0048] In Comparative Example 2, which used an aromatic ester alone in the base oil, premature abnormal flaking occurred in the hard acceleration/deceleration test. In Comparative Example 3, which used alkyldiphenyl ether oil alone in the base oil, premature seizure occurred in the high-speed, high-load endurance test. In Comparative Example 4, which used a diurea compound (cycloaliphatic diurea compound) having no aromatic hydrocarbon groups as a thickening agent, which was not in the predetermined range, abnormal flaking developed in the hard acceleration/deceleration test. Comparative Example 5, which used alkyldiphenyl ether oil and pentaerythritol ester as the base oil, was inferior in any of the high-temperature, high-speed endurance test, hard acceleration/deceleration test, and high-speed, high-load endurance test. Comparative Example 6, which used alkyldiphenyl ether oil and poly-α-olefin, was inferior in the high-temperature, high-speed endurance test.

[0049] In contrast, Examples 1-5 in which a grease is used in which alkyldiphenyl ether oil and aromatic ester oil were blended in the predetermined range as the base oil, an aromatic diurea compound and a cycloaliphatic diurea compound were added as thickening agents in the predetermined range, and a passivating agent was added, showed superior results in any of the high-temperature, high-speed endurance test, hard acceleration/deceleration test, and high-speed, high-load endurance test.

[0050] In the heat-resistant, high-speed, high-load rolling bearing of this invention a grease composition is sealed in which as a base oil, alkyldiphenyl ether oil and aromatic ester oil are mixed at a predetermined ratio, and a diurea-family thickening agent and a passivating agent are added. Thus, it is extremely superior in the supply ability of a lubricating oil to frictional surfaces and prevention of oxidative deterioration of grease. Thus, a heat-resistant, high-speed, high-load rolling bearing for automotive accessories and electric parts is provided in which no abnormal flaking occurs, the life is sufficiently long and the durability is superior.

[0051] Also, if an aromatic ester oil having a predetermined dynamic viscosity is used for the grease composition, a heat-resistant, high-speed, high-load rolling bearing will be provided in which abnormal flaking hardly occurs and which is superior in durability.

[0052] In the grease composition for a rolling bearing according to this invention, because the above-described predetermined base oil and thickening agent are added, a grease composition will be provided which is sufficiently supplied to frictional surfaces and is long in life even under high-temperature, high-speed, high-load conditions when used in automotive accessories or electric parts such as an alternator, electromagnetic clutch, tension pulley or one-way clutch. Also because a predetermined amount of passivating agent is blended in the grease having the above properties, no abnormal flaking will occur even under high-temperature, high-speed, high-load conditions. Thus a durable grease composition is provided. TABLE 1 Example Comparative Example 1 2 3 4 5 1 2 3 4 5 6 Base oil Aromatic ester oil *1 39 15.6 15.6 40 16 15.6 78 — 41 — 62.4 (wt %) Alkyldiphenylether oil *2 39 62.4 62.4 40 64 62.4 — 78 41 54.6 — Ester oil *3 — — — — — — — — — 23.4 — Poly α olefin oil *4 — — — — — — — — — — 15.6 Thickener Isocyanate MDI 11.85 11.85 11.85 10.97 10.97 11.85 11.85 11.85 10.04 11.85 11.85 (wt %) Amine P-toluidine 10.15 10.15 10.15 4.61 4.61 10.15 10.15 10.15 — 10.15 10.15 Cyclohexylamine — — — 4.42 4.42 — — — 7.96 — — Additive Antioxidant *5 2 2 2 2 2 2 2 2 2 2 2 (wt %) Passivating agent *6 1 1 1 1 1 1 1 1 1 1 1 Test method {circle over (1)} 289 297 305 279 290 300 269 303 296 263 300 {circle over (2)} 2180 3020 3220 2360 2710 403 1540 2030 1770 790 800 {circle over (3)} 300< 300< 300< 300< 300< 220 160 300< 180 100 300< {circle over (4)} 1000< 1000< 1000< 1000< 1000< 310 370 208 840 170 1000< 

What is claimed is:
 1. A heat-resistant, high-speed, high-load rolling bearing in which is sealed a grease composition which comprises a base oil which is a mixture alkyldiphenyl ether oil and aromatic ester oil at the ratio (in weight) of 50:50 to 80:20, a diurea compound expressed by the following formula as a thickening agent, and 0.1 to 5 wt % of a passivating agent.

(wherein R₂ is an aromatic hydrocarbon group having a carbon number of 6-15, R₁ and R₃ are an aromatic hydrocarbon groups having a carbon number of 6-12 or a cycloaliphatic hydrocarbon group having a carbon number of 6-20. R₁ and R₃ may be identical to or different from each other.)
 2. The heat-resistant, high-speed, high-load rolling bearing as claimed in claim 1 wherein the rate of the aromatic hydrocarbon group relative to the total amount of R₁ and R₃ is 50-100 mol %.
 3. The heat-resistant, high-speed, high-load rolling bearing as claimed in claim 1 or 2 wherein said aromatic ester oil has a dynamic viscosity at 40° C. of 20 to 150 mm²/s.
 4. A grease composition for rolling bearings for use in automotive accessories or electric parts, the grease composition comprising a base oil which is a mixture alkyldiphenyl ether oil and aromatic ester oil at the ratio (in weight) of 50:50 to 80:20, a diurea compound expressed by the following formula as a thickening agent, and 0.1 to 5 wt % of a passivating agent.

(wherein R₂ is an aromatic hydrocarbon group having a carbon number of 6-15, R₁ and R₃ are an aromatic hydrocarbon groups having a carbon number of 6-12 or a cycloaliphatic hydrocarbon group having a carbon number of 6-20. R₁ and R₃ may be identical to or different from each other.)
 5. The grease composition as claimed in claim 4 wherein the rate of the aromatic hydrocarbon group relative to the total amount of R₁ and R₃ is 50-100 mol %.
 6. The grease composition for a rolling bearing as claimed in claim 4 or 5 wherein said accessory or electric part is an alternator, electromagnetic clutch, tension pulley or one-way clutch.
 7. The grease composition as claimed in claim 4 or 5 wherein said aromatic ester oil has a dynamic viscosity at 40° C. of 20 to 150 mm²/s. 